Late August/Early September Review of This Season’s Program Encouraged to Gauge Results by Steve Poindexter

In Michigan, Rhizoctonia root and crown rot is the most prevalent root disease in sugarbeet production. This disease in significant quantities will reduce tonnage, sugar content and can affect pile storage. Implementing the proper control management strategy can pay great dividends.

Generally, late August or early September is an excellent time to evaluate potential yield, quality and income losses from this disease. New strategies may need to be implemented for next year if assessment shows an economic loss. losses from this disease. New strategies may need to be implemented for next year if assessment shows an economic loss.

Michigan State University Extension-Sugarbeet Advancement would recommend that every sugarbeet field be evaluated for potential Rhizoctonia impact. This can easily be implemented by randomly flagging 100 feet of row in at least six (6) locations in each field. Count dead and dying beets in each location. Dead beet carcasses are easy to determine and often leave holes in the ground. Dying beets are normally very yellow, with roots either partially or completely covered with rot. These plants normally can be wiggled in the soil or can be easily kicked out of the ground. Often, beets can have some Rhizoctonia spots on the roots and appear to have normal foliar appearance. Visually detecting those plants is nearly impossible and should not be included in the counts.

The average amount of dead or dying beets should be determined from all locations. Refer to Table 1 to determine potential impact of Rhizoctonia in each field. This chart was developed by Jim Stewart, research agronomist with Michigan Sugar Company, combining both Michigan Sugar small trial data and Sugarbeet Advancement field trials. Multiple years, locations and varieties were combined to formulate these data. The Rhizoctonia level and impact is only an estimate and can vary depending on variety tolerance, population and growing season.

It is very important to recognize the Rhizoctonia resistance of the variety that is being evaluated. If there is even a “noticeable” amount in a field with a resistant variety, then it may end up a big problem with a susceptible “high yielding variety.” In the 2013 Sugarbeet Advancement Variety Trials, the Rhizoctonia dead beet counts for the hottest varieties were around 10 times higher than the most resistant varieties. This would give an indication of what Rhizoctonia levels could be if a grower switched to a susceptible variety without altering his management plan.

Conversely, some of the nematode varieties provide high yields. It may be better to have nematode tolerance and give up some yield to Rhizoctonia. Nematode-infested fields with a history of Rhizoctonia often do best with a nematode-tolerant variety and two Quadris® applications. (Michigan growers can refer to the REACh Variety Trial results for variety resistance.)

If the disease impact is greater than desired, then next year’s management plan may need to be altered. This may include applying Quadris either in-furrow or foliar, if you are not applying Quadris already. Consider a two spray system which includes infurrow and a 6-8 leaf application. This option has, over time, given the most consistent positive results. Switching to a more tolerant Rhizoctonia variety in combination with a Quadris spray program will give very good results, particularly under heavy disease pressure. Select varieties carefully, as some of the most tolerant varieties may lack genetically in yield and quality or in nematode tolerance.